Controlled crying improves infants' sleep, reduces mothers' depression and does not cause any long-term harm, a Melbourne study has shown.

Researchers from the Murdoch Childrens Research Institute analysed outcomes at six years for children whose parents used behavioural techniques to regulate their sleeping as infants.

The techniques - designed to teach babies to fall asleep by themselves - included controlled crying, in which parents put their baby to bed tired and left them for short periods even if they cried, returning to reassure and settle them if necessary. Another technique adopted by parents in the study was ''camping out'', in which a parent sat next to their baby's cot on a chair while the baby fell asleep and the parent slowly moved out of the room in a gradual process over a few weeks.

Writing in the journal Paediatrics, the researchers said there was strong evidence that the techniques reduced infant sleep problems and associated maternal depression for up to 16 months afterwards.

But they said unproven concerns about potential long-term effects on children's mental health had provoked vigorous debate and limited uptake of the techniques, despite their effectiveness. Their study, the first to follow up children as late as age six, compared outcomes for children whose parents used the behavioural techniques at age eight to 10 months to those whose parents did not.

The researchers found there were no differences in the mental and behavioural health, stress levels, and relationships of children across the two groups five years later.

Lead researcher Anna Price said parents and health professionals should therefore feel confident about the effectiveness and safety of sleep interventions in infants aged six months and older.

The researchers said information currently available to parents about the effects of behavioural sleep strategies was inconsistent and in some cases outdated, and should be updated.

Dr Price said infant sleep problems were widespread and had a significant effect on families. ''It's really important to conduct these studies so you can get the evidence and reassure families that what they are doing is going to help and it's not going to harm,'' she said.

Among the participants in the study was Georgie Girardau, who found controlled crying a highly effective technique for her twins Thomas and Rachel, now healthy nine-year-olds.